The functions of the laboratory Core are: 1. to provide Individual Projects #1 and #2 with accurate and reproducible measurements of the levels of cortisol and melatonin in saliva samples. These non-invasive measurements will allow for th estimation of the onset of nocturnal melatonin secretion, a marker of circadian phase which is affected by the aging process, and the quiescent period of cortisol secretion, a marker of hypothalamo-pituitary-adrenal function which is affected by aging, stress and sleep loss. In contrast to plasma levels, saliva levels of cortisol reflect the concentrations of the free hormone, rather than the combination of free and bound hormone. 2. to provide Individual Project #2 with accurate and reproducible measurement of the levels of melatonin and thyroid-stimulating-hormone (TSH) in plasma samples collected in research subjects admitted to the University of Chicago Clinical Research Center. The Core laboratory will also prepare samples for the assay of blood levels of other hormones too be performed in the Laboratory of the Clinical Research Center and/or in the Diabetes Research and Training Center of th University of Chicago. 3. to provide Individual Project #3 with accurate and reproducible measurements of the levels of melatonin in blood samples collected from hamsters. 4. to provide Projects #1 and #2 with accurate and reproducible measurements of the plasma levels of catecholamines (epinephrine, norepinephrine and dopamine). The laboratory Core utilizes the existing facilities of the PI, Dr. Scherberg, and the Co-PI, Dr. Polonsky, at the University of Chicago. Both investigators have extensive experience in performing measurements for circadian rhythm studies. The availability of the major equipment needed to perform these measurements reduces the overall cost of these services to the program Project. The Core laboratory centralizes records on all hormonal measurements obtained in studies performed under the auspices of the Program Project.